Split phase inverters for CCFL backlight system

Abstract

An apparatus and method for driving a lamp are provided. In one embodiment, an inverter having four switching elements is split into two inverter arms that are deployed at separate terminals of a floating lamp structure to achieve even light output. A controller drives both inverter arms such that power switching lines do not cross the floating lamp structure. In one embodiment, the controller adjusts the brightness of the lamp structure by adjusting the phase difference between outputs of a first inverter arm relative to a second inverter arm. In one embodiment, the controller adjusts the brightness by symmetrically pulse width modulating the outputs of the first inverter arm and the second inverter arm.

What is claimed is: 
     
       1. An inverter comprising:
 a first transformer; 
 a second transformer, wherein a lamp structure is coupled in a floating configuration between a secondary winding of the first transformer and a secondary winding of the second transformer; 
 a first two-switch network configured to generate a first alternating current signal across a primary winding of the first transformer; 
 a second two-switch network configured to generate a second alternating current signal across a primary winding of the second transformer; and 
 a controller configured to control the first two-switch network and the second two-switch network, wherein at least one of the first two-switch network and the second two-switch network is controlled by a first control signal and an inverted version of the first control signal with dead time inserted at transitions between switching states. 
 
     
     
       2. The inverter of  claim 1 , wherein the first two-switch network and the second two-switch network have respective topologies selected from the group comprising a half-bridge configuration, a push-pull configuration, and a push-pull forward configuration. 
     
     
       3. The inverter of  claim 1 , wherein the controller is configured to symmetrically adjust pulse widths of the first alternating current signal and the second alternating current signal. 
     
     
       4. The inverter of  claim 1 , wherein the controller is configured to adjust a phase difference between the first alternating current signal and the second alternating current signal. 
     
     
       5. The inverter of  claim 4 , wherein the first alternating current signal and the second alternating current signal, respectively, have approximately fifty percent duty cycles. 
     
     
       6. The inverter of  claim 1 , wherein the lamp structure comprises a first fluorescent lamp coupled between a first terminal of the secondary winding of the first transformer and a first terminal of the secondary winding of the second transformer. 
     
     
       7. An inverter comprising:
 a first transformer; 
 a second transformer, wherein a lamp structure is coupled in a floating configuration between a secondary winding of the first transformer and a secondary winding of the second transformer, and the lamp structure comprises:
 a first fluorescent lamp coupled between a first terminal of the secondary winding of the first transformer and a first terminal of the secondary winding of the second transformer; and 
 a second fluorescent lamp coupled between a second terminal of the secondary winding of the first transformer and a second terminal of the secondary winding of the second transformer; 
 
 a first two-switch network configured to generate a first alternating current signal across a primary winding of the first transformer; 
 a second two-switch network configured to generate a second alternating current signal across a primary winding of the second transformer; and 
 a controller configured to control the first two-switch network and the second two-switch network. 
 
     
     
       8. The inverter of  claim 6 , further comprising at least a second fluorescent lamp coupled in parallel with the first fluorescent lamp. 
     
     
       9. The inverter of  claim 8 , wherein a second terminal of the secondary winding of the first transformer is coupled to a second terminal of the secondary winding of the second transformer. 
     
     
       10. The inverter of  claim 9 , wherein the second terminal of the secondary winding of the first transformer is grounded. 
     
     
       11. An inverter comprising:
 a first power transformer; 
 a second power transformer, wherein at least one lamp is coupled between the first power transformer and the second power transformer; 
 split switching arms, wherein one of the split switching arms is dedicated to the first power transformer and another of the split switching arms is dedicated the second power transformer; and 
 a controller to control the split switching arms to produce symmetric alternating current (AC) waveforms in the first and second power transformers to drive the at least one lamp, wherein at least one of the split switching arms is controlled by a first control signal and an inverted version of the first control signal with dead time inserted at transitions between switching states. 
 
     
     
       12. The inverter of  claim 11 , wherein each of the split switching arms comprises a two-switch network. 
     
     
       13. The inverter of  claim 12 , wherein the first and second power transformers each comprises a primary winding, and wherein the two-switch network is a half-bridge network comprising:
 two transistors coupled in series across a supply voltage, wherein the two transistors are interconnected at a switching node; and 
 a capacitor coupled to the switching node, wherein the capacitor is configured to AC couple the switching node to the primary winding. 
 
     
     
       14. An inverter comprising:
 a first power transformer; 
 a second power transformer, wherein at least one lamp is coupled between the first power transformer and the second power transformer; 
 split switching arms, wherein one of the split switching arms is dedicated to the first power transformer and another of the split switching arms is dedicated the second power transformer and wherein each of the split switching arms comprises a two-switch network; 
 a controller to control the split switching arms to produce symmetric alternating current (AC) waveforms in the first and second power transformers to drive the at least one lamp; and 
 wherein at least one of the first and second power transformers comprise a primary winding having a center tap coupled to a first direct-current (DC) voltage signal, and wherein the two-switch network is a push-pull network comprising:
 a first transistor coupled between a second DC voltage signal and a first terminal of the primary winding; and 
 a second transistor coupled between the second DC voltage signal and a second terminal of the primary winding. 
 
 
     
     
       15. An inverter comprising:
 a first power transformer; 
 a second power transformer, wherein at least one lamp is coupled between the first power transformer and the second power transformer; 
 split switching arms, wherein one of the split switching arms is dedicated to the first power transformer and another of the split switching arms is dedicated the second power transformer and wherein each of the split switching arms comprises a two-switch network; 
 a controller to control the split switching arms to produce symmetric alternating current (AC) waveforms in the first and second power transformers to drive the at least one lamp; and 
 wherein at least one of the first and second power transformers comprise a first primary winding and a second primary winding, and wherein the two-switch network is a push-pull forward network comprising:
 a first semiconductor switch coupled between a first direct-current (DC) voltage signal and a first terminal of the first primary winding, wherein a second terminal of the first primary winding is coupled to a second DC voltage signal; and 
 a second semiconductor switch coupled between the second DC voltage signal and a first terminal of the second primary winding, wherein a second terminal of the second primary winding is coupled to the first DC voltage signal. 
 
 
     
     
       16. The inverter of  claim 15 , wherein the push-pull forward network further comprises a capacitor coupled between the first terminal of the first primary winding and the first terminal of the second primary winding. 
     
     
       17. A method for driving a lamp, the method comprising:
 driving a first terminal of a lamp with a first dedicated two-switch network, wherein the first dedicated two-switch network is controlled by a first control signal and an inverted version of the first control signal with dead time inserted at transitions between switching states; 
 driving a second terminal of the lamp with a second dedicated two-switch network, wherein the second dedicated two-switch network is controlled by a second control signal and inverted version of the second control signal with dead time inserted at transitions between switching states; and 
 symmetrically controlling the first dedicated two-switch network and the second dedicated two-switch network using a common controller. 
 
     
     
       18. The method of  claim 17 , wherein driving the first terminal and the second terminal of the lamp comprises phase-shift modulating a first signal provided to the first terminal relative to a second signal provided to the second terminal. 
     
     
       19. The method of  claim 17 , wherein driving the first terminal and the second terminal of the lamp comprises pulse-width modulating a first signal provided to the first terminal and a second signal provided to the second terminal, wherein the first signal and the second signal are substantially symmetrically pulse-width modulated with respect to each other. 
     
     
       20. A backlighting system comprising:
 a first lamp structure having a first end and a second end; 
 a first two-transistor network dedicated to providing a first alternating current (AC) signal to the first end; 
 a second two-transistor network dedicated to providing a second AC signal to the second end; and 
 a first controller coupled to the first two-transistor network and the second two-transistor network, the first controller configured to correlate the waveform relations between the first AC signal and the second AC signal, and wherein at least one of the first two-transistor network and the second two-transistor network is controlled by a first control signal and an inverted version of the first control signal with dead time inserted at switch-over transitions between switching states. 
 
     
     
       21. The backlighting system of  claim 20 , wherein the first lamp structure comprises at least one cold cathode fluorescent lamp. 
     
     
       22. The backlighting system of  claim 21 , wherein the at least one cold cathode fluorescent lamp is in a floating configuration. 
     
     
       23. A backlighting system comprising:
 a first lamp structure having a first end and a second end; 
 a first two-transistor network dedicated to providing a first alternating current (AC) signal to the first end; 
 a second two-transistor network dedicated to providing a second AC signal to the second end; 
 a first controller coupled to the first two-transistor network and the second two-transistor network, the first controller configured to correlate the waveform relations between the first AC signal and the second AC signal; 
 a second controller in communication with the first controller, wherein the first controller is configured to control the second controller; 
 a second lamp structure; 
 a third two-transistor network dedicated to providing a third AC signal to the second lamp structure; and 
 a fourth two-transistor network dedicated to providing a fourth AC signal to the second lamp structure, wherein the second controller is configured to correlate the waveform relations between the third AC signal and the fourth AC signal based at least in part on the first controller.